PatriotForge Backend Patterns

Stack: FastAPI · Python 3.12 · SQLAlchemy 2.x (async) · Pydantic v2 · Redis 7 · PostgreSQL 15

Project Layout

backend/
├── app/
│   ├── main.py          # create_app() factory + lifespan
│   ├── config.py         # Settings(BaseSettings) — env-driven
│   ├── routers/          # one file per module (auth.py, quotes.py, …)
│   ├── services/         # pure business logic — no HTTP objects
│   ├── schemas/          # Pydantic request/response models
│   ├── models/           # SQLAlchemy ORM models
│   └── deps.py           # dependency injection functions
├── tests/                # pytest-asyncio tests
├── alembic/              # database migrations
└── pyproject.toml

Router Pattern

router = APIRouter(prefix="/api/auth", tags=["auth"])

@router.post("/login", response_model=LoginResponse, status_code=200)
async def login(
    data: LoginRequest,
    db: AsyncSession = Depends(get_db_session),
    redis: Redis = Depends(get_redis),
    request: Request, response: Response,
): ...

• •Always declare response_model, status_code, explicit Depends()
• •Router calls service layer — no business logic in routers

Service Layer

• •Pure async functions — accept db session, redis, domain objects
• •Raise domain exceptions (DuplicateEmail, InvalidCredentials), not HTTPException
• •Routers catch domain exceptions and map to HTTP status codes

Pydantic v2

• •Requests: model_config = ConfigDict(extra='forbid') — reject unknown fields
• •Responses: model_config = ConfigDict(from_attributes=True) — ORM compatibility
• •Validate string lengths, use SecretStr for passwords

SQLAlchemy Models

• •Use Mapped[] type annotations + mapped_column()
• •Table names: forge_ prefix (e.g., forge_users)
• •UUID primary keys: mapped_column(UUID, primary_key=True, default=uuid4)
• •Always include: created_at, updated_at, deleted_at

Dependency Injection

• •get_db_session(): yields AsyncSession from app.state.async_session_factory
• •get_redis(): returns app.state.redis
• •State-based injection makes testing trivial (swap state in test app)

App Factory

• •create_app(settings) builds the app — test-friendly, no module-level singletons
• •Lifespan context manager initializes DB engine, Redis, runs Alembic check

Conventions

• •All I/O is async — no sync DB calls
• •Strict mypy, ruff formatting, 100-char line limit
• •Never use sed/awk for file editing

📖 Reference files: backend/app/routers/auth.py, backend/app/services/auth.py, backend/app/schemas/auth.py